EFFECTS OF INSULIN AND EXERCISE ON AMINO-ACID-TRANSPORT IN RAT SKELETAL-MUSCLE

In the present study, the initial rates of amino acid transport by iso lated rat skeletal muscle plasma membrane vesicles mere investigated. This approach facilitates the study of the transport of naturally occu rring amino acids independent of the effects of cellular metabolism. A lanine and glutamine influxes were measured using a rapid filtration t echnique. Transport was examined in the presence and absence of Na and the properties of membranes from control, insulin-treated, or acutely exercised rats were studied. Both alanine and glutamine were transpor ted by Na-dependent processes. The values for maximum rate of transpor t (V-max) for Na-dependent alanine and glutamine transport were 203 an d 224 pmol.mg(-1).s(-1), respectively. The K-1/2, values mere 2.9 mM a lanine and 1.9 mM glutamine. The V-max for Na-dependent alanine transp ort was increased by insulin treatment of the animal and by acute exer cise. 2-(Methylamino)-isobutyric acid (MeAIB) partially inhibited the control Na-dependent alanine influx and completely inhibited the incre ase due to insulin or exercise treatment, indicating the importance of both system A and a non-system A, Na-dependent carrier for alanine tr ansport. The V-max for Na-dependent MeAIB uptake was also increased by insulin or exercise treatments of the rats. Unlike alanine, Na-depend ent glutamine transport was not affected by insulin.